The foremost objective of this proposal is to develop a specific, sensitive and reliable assay for the serodiagnosis of filarial nematode infections. The Dirofilaria immitis-dog system will be used as a model for the development of such an assay. Emphasis will be placed on the detection of specific soluble circulating antigen and on the detection of specific antibody in infected dogs. The development of enzyme-linked and fluorometric assays, both adequate for antigen or antibody detection, is proposed. Soluble circulating antigens will be recovered from infected dogs, metabolic antigens will be isolated from immunologically compromised animals and somatic and cuticular antigens will be purified from adults and microfilariae to effect the principal objective. In addition to the recovery of antigens for use in these assays, the antigens will be partially characterized to facilitate future purification of antigens from the D. immitis-dog system or human filarial systems.